Magnetoresistive (MR) devices undergo electrical resistance changes when an external magnetic field is applied. Such devices have numerous applications, including as the reader portion of a magnetic read head in a magnetic data storage and retrieval system, for example a computer disk drive. One type of reader used in disk drives is a tunneling magnetoresistive (TMR) sensing element, which typically includes a sensing element made of a series of layers. For example, a sensing element may include a sensor material layer sandwiched between a pinned magnetic layer and a free magnetic layer. The sensing element may be disposed between first and second nonmagnetic gap layers. The first and second gap layers can be located between ferromagnetic first and second shield layers while first and second lead layers are connected to the sensing element for conducting a sense current. When the sensing element is subjected to positive and negative signal fields from tracks on a rotating magnetic disk in a disk drive, the resistance of the read sensor changes. These resistance changes cause potential changes in the sense current circuit, which are processed as playback signals by processing circuitry.
A typical magnetic read head for use with a disk drive has an exterior head surface which faces the rotating magnetic disk and is supported on swirling air from the rotating disk which is referred to as an air bearing. For this reason, the exterior head surface is referred to as an air bearing surface. The sensing element has a back edge which is recessed in the read head opposite the air bearing surface. The back edge is precisely located by photolithography processing.
During construction, the air bearing surface is precisely defined so that the sensing element has a precise stripe height which is the distance between the air bearing surface and the back edge. This is accomplished by lapping the wafer substrate on which the magnetic read head is constructed. To achieve precise and accurate control of the depth to which the sensing element is lapped, an electronic lapping guide is typically included on the wafer substrate with the sensing element during manufacture. The wafer substrate is then diced into rows and then lapped until the air bearing surface has been precisely formed. The electrical resistance of the electronic lapping guide is inversely proportional to the height of the sensor. Thus, monitoring of the electronic lapping guide resistance during lapping permits very fine tuned control of the stripe height of the sensing element. For example, the lapping process can be controlled to cease when the electronic lapping guide resistance reaches a calculated value associated with a desired stripe height of the sensing element.
The magnetic read head can also include a flux guide formed of a soft magnetic material which guides leakage fluxes from the disc medium towards the sensing element. The flux guide also enables the sensing element to be formed away from the air bearing surface, thereby preventing a short circuit from occurring when the tip of the element becomes exposed to the air bearing surface.